1. Field of the Invention
The present invention generally relates to polygonal mirror units, optical scanning apparatuses and bar code readers, and more particularly to a polygonal mirror unit having reflection surfaces arranged with a high accuracy, and an optical scanning apparatus and a bar code reader which use such a polygonal mirror unit.
2. Description of the Related Art
Optical apparatuses such as laser printers and laser scanners are provided with a scan mechanism which causes a light beam emitted from a light beam to scan. The scan mechanism in many cases includes a polygonal mirror unit which is rotated by a motor.
The polygonal mirror unit includes a plurality of reflection surfaces, that is, mirror surfaces. As the polygonal mirror unit undergoes one revolution by being rotated by the motor, it is possible to make a number of scans equal to the number of reflection surfaces of the polygonal mirror unit. For this reason, the polygonal mirror unit is often used in apparatuses which require high-speed scans to be made.
Generally, there are demands to reduce the size, weight and cost of apparatuses, including optical apparatuses such as laser printers and laser scanners. Consequently, there are strong demands to also reduce the size, weight and cost of the polygonal mirror unit.
Conventional polygonal mirror units are constructed as follows.
According to a first conventional polygonal mirror unit, a base has a plurality of surfaces, and a reflection mirror is adhered on each of the surfaces of the base by use of an adhesive agent or an adhesive tape. The base is molded from a resin or, is formed from a metal or the like.
On the other hand, according to a second conventional polygonal mirror unit, a base having a plurality of surfaces corresponding to reflection surfaces is molded from a resin, and the reflection surfaces are formed on the surfaces of the base by evaporation. For example, aluminum is used as the material forming the reflection surfaces. The evaporation of the aluminum to form the reflection surfaces can be carried out simultaneously with respect to a plurality of bases.
However, the following problems exist in the conventional polygonal mirror units.
According to the first conventional polygonal mirror unit, it is necessary to adhere the reflection mirrors one by one onto the corresponding surfaces of the base. As a result, there are problems in that a large number of steps are required to make the polygonal mirror unit, and the production cost of the polygonal mirror unit is high.
In addition, in optical scanning apparatuses, there are demands to improve the accuracy of the dimensions of various parts of a scan mechanism, because the dimensions of the various parts determine the performance of the optical scan apparatus. The polygonal mirror unit is no exception. But according to the first conventional polygonal mirror unit, there are problems in that it is difficult to secure a sufficiently high accuracy with which the reflection mirrors are adhered onto the corresponding surfaces of the base, and it requires a skilled person to adhere the reflection mirrors on the surfaces of the base.
On the other hand, the second conventional polygonal mirror unit is made by the steps of integrally molding the base from the resin, and forming the reflection surfaces by evaporation. Hence, the number of steps required to make the second conventional polygonal mirror unit is smaller than that required to make the first conventional polygonal mirror unit. However, the following problems are introduced when molding the base from the resin.
That is, as a general problem introduced upon resin molding, deforming or warping of the molded resin part after being cooled is inevitable due to contraction of the resin. In the case of the polygonal mirror unit, the scan of the light beam is generated by the reflection of the light beam by the reflection surface, and the planar accuracy of each of the reflection surfaces greatly affects the performance of the optical scan. However, when the planar accuracy of the reflection surfaces deteriorates due to the distortion or warp of the molded resin base particularly at the reflection surfaces, there is a problem in that a desired performance cannot be obtained by the optical scan unit which uses such a polygonal mirror unit.
Therefore, the conventional polygonal mirror units have problems from the point of view of the high production cost and poor performance.
Accordingly, it is a general object of the present invention to provide a novel and useful polygonal mirror unit, optical scanning apparatus and bar code reader, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a polygonal mirror unit, optical scanning apparatus and bar code reader, which can be produced at a relatively low cost and can realize a high planar accuracy of reflection surfaces as compared to the conventional polygonal mirror unit, optical scanning apparatus and bar code reader which use a molded resin base having reflection surfaces formed thereon by evaporation.
Still another object of the present invention is to provide a polygonal mirror unit having a base with a plurality of reflection surfaces, comprising a plurality of mirrors which have upper ends and lower ends and forms the reflection surfaces, a first base part having first grooves which receive the lower ends of the mirrors, and first stoppers which push the mirrors towards an outside of the first base part, and a second base part having second grooves which receive the upper ends of the mirrors, and second stoppers which push the mirrors towards an outside of the second base part, where the first and second base parts are connected to form the base. According to the polygonal mirror unit of the present invention, the polygonal mirror unit can be produced at a relatively low cost and it is possible to realize a high planar accuracy of the reflection surfaces as compared to the conventional polygonal mirror unit which uses a molded resin base having reflection surfaces formed thereon by evaporation.
A further object of the present invention is to provide an optical scanning apparatus comprising a light source which emits a light beam, and a polygonal mirror unit which rotates and has a base with a plurality of reflection surfaces which reflect the light beam from the light source to generate a scanning line beam, where the polygonal mirror unit comprises a plurality of mirrors which have upper ends and lower ends and forms the reflection surfaces, a first base part having first grooves which receive the lower ends of the mirrors, and first stoppers which push the mirrors towards an outside of the first base part, and a second base part having second grooves which receive the upper ends of the mirrors, and second stoppers which push the mirrors towards an outside of the second base part, and the first and second base parts are connected to form the base. According to the optical scanning apparatus of the present invention, the polygonal mirror unit can be produced at a relatively low cost and it is possible to realize a high planar accuracy of the reflection surfaces as compared to the conventional polygonal mirror unit which uses a molded resin base having reflection surfaces formed thereon by evaporation.
Another object of the present invention is to provide a bar code reader comprising a housing having a columnar shape with a generally flat front face, a generally semicircular rear face, and top and bottom surfaces, a pair of bearing parts respectively provided on the top and bottom surfaces of the housing, an optical unit which emits a scanning light beam, a reading window provided in the front face of the housing and transmitting the scanning light beam outside the housing, a display part, and a switch integrally formed on the display part. According to the bar code reader of the present invention, it is possible to cope with various kinds of bar code reading operations, because the bar code reader can be easily be set up at different orientations to suit the needs.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.